Ambient temperature vs. engine temperature

[mark pruett]

I've read many posts on the forums advocating the use of higher viscosity oils in hot climates, say 10w-30 vs. 5w-30, or 10w-40 vs. 10w-30.

What I don't get(and correct me if I'm wrong), is that it seems to me that the temperature inside of an engine in operation and at operating temperatures will be pretty much independent of the outside temperature- that's what the cooling system is for, right?

In other words, it's not going to be any hotter inside a warmed up engine if it's 100 degrees outside or 30 degrees outside, because the thermostat will keep it in the right temperature range, provided the engine's not overheating.

And... non-scientific data (i.e. my truck's temp gauge) tend to bear this out- it seems pretty steady, regardless of whether I'm driving in summer or winter. (and no, it's not an idiot gauge either)

So why the fascination with varying the weight according to the seasons? I can understand using a 0w or 5w oil if you'll be somewhere cold, but using a 10w-30 instead of a 5w-30 in the summer just seems kind of dumb.

 

[Palut]

Water temperature does stay the same, the thermostat does a good job of keeping it constant. Most cars don't have oil coolers though, so there's no thermostat keeping the oil cool. On my car, for example, the only thing that cools the oil is the surface area of the oil pan. When its 40-50 degrees out, I see oil temps of about 190-200° F. When its in the 70s, I see 200-215. When its hotter, I see a little higher. When its 10-20°, I only see temps in the 170's (I've only driven this car in those low temps twice though).

While water temperature does stay constant with outside temperature, oil temperature usually doesn't.

 

[Ugly3]

Hot weather alone does not raise oil temps enough to require the use of a higher viscosity oil. If you are racing, towing heavy trailers, etc., then maybe a higher viscosity is needed.

 

[Gary Allan]

The fascination that you see is primarily with cold start issues between one weight over another. There is also the issue of not all 30 weights being created equal (the visc varys within the spec) and the VII employed to attain the 0w, 5w, and 10w cold specs. Ambient temp, as Palut asserts, can alter oil temp a decent amount ..enough to put it in another visc. If you don't reach 212°F ..and only hit 160 ..you're probably a grade higher in operating visc. You will probably be doing the same thing on a 10-14 mile commute in a common pushrod engine. It takes a long time to thremally saturate the common engine ..long after the coolant has reached 200°F+

 

[1911]

quote:

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Originally posted by Ugly3:
Hot weather alone does not raise oil temps enough to require the use of a higher viscosity oil. If you are racing, towing heavy trailers, etc., then maybe a higher viscosity is needed.

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Ugly3,

Now wouldn't that depend on how much hotter the oil got and what viscosity you are starting with before considering a change? Some cars already start with marginally thin oil for normal driving conditions/ambients. Palut ahead of you recorded operating temperature ranges varying as much as 50F. 50F is night and day in terms of operating viscosity, you may want to reconsider your blanket statement. Your point should not be taken as a general truth but is case dependent. With long idle times, (traffic jam scenario) where the water is not getting cooled efficiently, there can be some extreme oil temp behaviour with some cars.

1911

 

[1911]

quote:

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Originally posted by Ugly3:
Hot weather alone does not raise oil temps enough to require the use of a higher viscosity oil. If you are racing, towing heavy trailers, etc., then maybe a higher viscosity is needed.

---

Brilliant Ugly3,

Then why have millions of the cars that have been produced in this world had owners manuals with charts that recommend thicker oils for higher ambient temperature conditions. And please don't be foolish enough to respond with a "the thicker oils do better at start-up when it's warm out" because that would constitute another ridiculous statement. Even 5 weight basestocks are a good 10 times or so more viscous than they need to be with a 100F start. As a smart board member here always says "no oil is thin enough at start-up".

The answer is because of excessive thinning at high temperatures and that is why they have such charts Ugly!!!! Perhaps you've never seen one before or something like that?

1911

 

[Blue99]

quote:

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So why the fascination with varying the weight according to the seasons? I can understand using a 0w or 5w oil if you'll be somewhere cold, but using a 10w-30 instead of a 5w-30 in the summer just seems kind of dumb.

---

It's not a fascination, it's simply understanding the differences in the formulations and applying this to the application.

Take a look at the Current Pennzoil Data Sheet which actually lists Noack volatility numbers for the various grades.

Note that the 5W-30 has a 14.7 Noack and the 10W-30 has a 10.9 Noack. This is typical for many brands & just reflects the lower volatility of a 10W-30 base oil blend vs. a 5W-30 blend.

As far as heat, motor oil returning from the upper heat zones of the engine is only cooled by mixing with oil in the sump and the thermal transfer that occurs with the walls of the crankcase.

Outside air temps have a great effect on the cooling of the engine crankcase.

Anyone actually running an oil temp gauge will note the increase in oil temps on a 50 degree day compared to a 90 degree day.

 

[Throttlebender]

Well, I posted for recommendations for my A4 1.8T on another thread. What are the opnions of running for example: Mobile 1 0w-40 vs Mobile 1 5w-40 T&SUV? I assume the 0w would be better for winter but what about year round? Is the 0w better because of it being thinner at start up?

 

[n8wvi]

Under some conditions, I contend an oil CAN be too thin at startup. It's been discussed here on this board that the higher the HTHS of an oil, the thicker the film left behind. If I have a 40 mile commute, I'll take the 15w-40 with it's robust HTHS.

Dave

 

[Gary Allan]

quote:

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Then why have millions of the cars that have been produced in this world had owners manuals with charts that recommend thicker oils for higher ambient temperature conditions.

---

Welp, that would be fine anywhere else in the world but the USA. 5w-30 weight is about the only thing spec'd ...anywhere ..under most condition in a contemporary auto. Some are spec'd lighter. The usual response to severe conditions is shorter intervals ..not a different weight. There are exceptions, naturally but they are few for gasoline (pushrod) engines.

Although ambient temp, in my experience, can surely effect oil temp to a degree, I don't know how it works on the "ceiling" as much as it does on the basement, so to speak. That is, I have personally seen a 20°F elevation over a 40° change in ambient (160F continuous vs. 180 continuous) ..but the impact is out of proportion.

btw- my experience shows that idling doesn't elevate oil temps. Perhaps biefly when you're coming off of a high rate of thermal combustion input ..like getting off of a highway ..but it usually calms down. The same thing is happening to the cooling system ..except that it is regulated and has more utilities to reject heat.

I do agree, however, that there is a "case by case" impact on oil temps ..but as far as our manufacturers are concerned (mostly) it doesn't have a lot to do with our oil selection in our common passenger cars and light duty gasoline trucks

If you've ever seen the publication that is reputed to be the strongest written document against evolution, it points out that a cow and a horse have different teeth, yet exist on the same grass field without difficulty in terms of feeding themselves.

My personal research, albiet limited, has shown that my engine can use 5w-20 through 20w-50 without difficulty over a broad range of ambient temps. Pressures, temps, etc. ...all fullfill the minimum daily adult requirement for oil nurishment.

So essentially, I kinda agree with Ugly3 there that I don't think our oil temps get too out of whack in regard to ambient temps ..at least for the most part

[ July 16, 2005, 08:57 PM: Message edited by: Gary Allan ]

 

[Ignatz]

Mark, on my 93 M-B the temperature gauge rises to a certain level at 70 deg. F. As the outside temperature rises, the gauge rises accordingly. Not much, but it does go up and down according to the outside temp. The engine temperature gauge on my car is in celcius and the outside temperature is in F. Right now I'm running Shell formula straight 30wt. with 5oz. of Valvoline syn oil treatment. I normally run 20-50 this time of the year. The only thing I notice different between 30wt. and 20-50 is the 20-50 has a little more oil pressure at idle when fully hot.

 

[Bryanccfshr]

I am with Gary and Ugly on this topic,
Certain vehicles have better regulation than others.. I don't own a vehicle wiothout some sort of stock oil cooler. I didn't so this on purpose, that's just the way my random purchases came ouot.. Even a cheap little mitsubishi suv has an oil cooler. MuTo pickem up truck has a coolant regulated oil heater/cooler.

So if your oil temperature is affected by ambient temperatures either add auxileray cooling or go up a grade when the ambient is Hot enough to require it.

This is not a one size fits all answer. I believe we need to know the engine and behaviors intimately when making choices such as these. Then there is the matter of thermal build up due to friction in more viscos oils.

 

[jsharp]

quote:

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Originally posted by 1911:

quote:

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Originally posted by Ugly3:
Hot weather alone does not raise oil temps enough to require the use of a higher viscosity oil. If you are racing, towing heavy trailers, etc., then maybe a higher viscosity is needed.

---

Ugly3,

Now wouldn't that depend on how much hotter the oil got and what viscosity you are starting with before considering a change? Some cars already start with marginally thin oil for normal driving conditions/ambients. Palut ahead of you recorded operating temperature ranges varying as much as 50F. 50F is night and day in terms of operating viscosity, you may want to reconsider your blanket statement. Your point should not be taken as a general truth but is case dependent. With long idle times, (traffic jam scenario) where the water is not getting cooled efficiently, there can be some extreme oil temp behaviour with some cars.

1911

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The only recent vehicle I've owned that had an oil temperature gauge showed lower oil temps sitting in traffic on a hotter day than running hard on the highway on a cooler day. The worst case was running the engine hard on a hot day of course.

Engine load seemed to be at least as much a factor that drove the oil temp as ambient temperature...

 

[1911]

Thanks Guys,

If you read my first post, I said whether or not grades should be upped is a case dependent issue. It appears from most of the subsequent posts that you agree with me on this. The one who is clearly out of line with this case dependent idea is Ugly3 who made a blanket statement in contradiction with most the vast majority of owners manuals ever produced in this world.

And Gary Allen, you should know that up until more recent years in the U.S., our manuals also had the "up the viscosity with temperature" charts in the manuals. I suspect in most cases, there is good reason for this. Then suddenly, only pretty much in the U.S, these charts disappeared. Gary, aren't the engines pretty much exactly the same anyway whether they are a 1.8T Volkswagen, 2.0 Mazda MZR, 1.6 Honda, etc running in Japan, Australia, Europe, U.S.? Why have their manuals for the exact same engines kept the temperature charts but the U.S. ones have not? In fact, even the exact same engines in the US had the chart on eyear and then it disappered on next years model year. With this reasoning in mind, your insinuation that that the manufacturers don't think ambient temperature should play a role in optimal viscosity selection for US cars is quite wrong. The paperwork is just missing and that ought to make all of you start asking good questions. I think you knew this Gary cause you're too smart not to, you were just playing devil's advocate but he's not working this Sunday.

And as far as idling is concerned, I don't doubt what any of you say with modern cooling systems. The flux of heat energy (joules per minute) that the engine puts into the lubricant and water is certainly way lower when the engine is idling versus being under load and much less fuel per unit time is being burned. But the ability to dissipate the heat generally drops too with reduced airflow. So it becomes very dependent on the cooling fan and cooling system characteristics. Many older cars seemed to get a lot more oil cooling (especially in the old days when cars were way off the ground and had no plastic undercarriage under the engine) from airflow under the car. These cars also tended to overheat more often in traffic jams and the like.

1911.......a .45 ACP solution to dealing with those who publish communisitic owner's manuals

 

[XS650]

quote:

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Originally posted by jsharp:
The only recent vehicle I've owned that had an oil temperature gauge showed lower oil temps sitting in traffic on a hotter day than running hard on the highway on a cooler day. The worst case was running the engine hard on a hot day of course.

Engine load seemed to be at least as much a factor that drove the oil temp as ambient temperature...

---

That's close to my casual observations, but it depends on which vehicle.

I've had oil temp gauges in a variety of cars, a couple of pick-ups and a motorcycle since the 1960s.

Engine load, ambient temperature, coolant temperature and vehicle speed all have significant effects. Which was most important seemed to vary by vehicle.

 

[1sttruck]

Cars with electric fans due to transverse mounted engines might be moe prone to getting hotter when idling in hot weather, as the duty cycle is designed to balance cooling with engine and electrical load. Our older Taurus tends to exhibit this, but I'll see how the new thermostat and coolant due this summer.

The diesel truck has very good cooling capacity, to the point that one needs to use a 'winter front' to cover part of the radiator in very cold weather. This is expected due to the need for cooling a turbodiesel that may be working hard pulling heavy loads. Ambient temps matter a lot as the sump holds three gallons, which takes awhile to warm in cold weather. It's also why a block heater is provided, and I still find it funny to be 'plugging in the truck' when it gets cold.

My most memorable experience with cold oil was a summer camping trip below Mt Whitney, several thousand feet up. You're pretty much running thru desert with Death Valley to the east and the incredible sight of the eastern slopes of the Sierras to the west, so a friend opted for something like a 50w or 60w oil in the Harley, per the shop recommendation. At our camp site it didn't get that hot but did freeze at night. When we were ready to leave I kicked the RD400 thru a few times, turned on the ignition and it fired right up. He could barely get the kick starter into position on the Sportster, and when he jumped on it the kick start just oozed down slowly with him standing on it. An hour next to the fire got it going :^)

 

[Geoff]

Most of it is probably load based as well as sump capacity. Think big car with small engine, poor aerodynamics and 4 qt sump capacity. At 70 mph, there might be a lot of constant load that isn't spread out among a big oil capacity.

Mercury Marine, the largest buyer of GM marine engines (all based on current vortec truck engines), does not allow 30 grade at temps over 50F per my owner's manual. These engines see constant high load with stock size sumps and oil coolers. Interestingly, 50 grades are not recommended either for any temp range.

Europeans, who pride themselves with cars that sustain being driven flat out, have been slower to recommend anything less than xw-40. Most American engines are just not designed to do this (there are lots of stories of American engines failing European testing when tried), and my view is that the recommendations are based on 80/20 rule and CAFE. ie, 80% of drivers will not run their engines hard enough to justify higher viscosity. This assumption is probably quite true, and those drivers can take the fuel economy benefits thinner oils offer.

Some engines have "hot spots" more predominantly than others that make volatility more of an issue, leading to sludge or deposits.

Some engines also may be more sensitive to viscosity due to oil system design. eg, is it high pressure or more flow based (let the oil drip down or get flung over the internals).

 

[XS650]

quote:

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Originally posted by 1sttruck:
Cars with electric fans due to transverse mounted engines might be moe prone to getting hotter when idling in hot weather,

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Same with my 96 Corvette. It has electric fans that don't come on until the coolant is over 220 for the 1st fan and about 230 for the second fan.

 

[427Z06]

quote:

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Originally posted by XS650:
That's close to my casual observations, but it depends on which vehicle.

I've had oil temp gauges in a variety of cars, a couple of pick-ups and a motorcycle since the 1960s.

Engine load, ambient temperature, coolant temperature and vehicle speed all have significant effects. Which was most important seemed to vary by vehicle.

---

Your experiences mirror mine. And I'll add, that even with identical vehicles, the simple addition of a thermostatically controlled oil cooler can change the equation significantly.

 

[Big O Dave]

1911, I might add that since a lot of those charts were published, oil has gotten a LOT better, and no longer do you have to run such high viscosities to protect against wear caused by oil thinning out.